Prior art power supplies may suffer from one or more of the following disadvantages:                excessive heat generated from power dissipated in dissipative components;        excessive current and/or voltage ripple in the load;        low power factor;        poor efficiency.        
A common solution to maintain both high power factor and low current ripple is to use a two-stage power supply. The first stage satisfies the requirements for high power factor by matching the current drawn to the applied voltage and the second stage powers the load with regulated low ripple in the current or the voltage. In lighting applications it is necessary to achieve these functions at the lowest possible cost and greatest achievable efficiency. A single stage supply can provide good power factor or good load regulation, but typically not both unless extremely large capacitors are added to the design.
Some recent studies have suggested the use of non-cascading structures for power factor correction switching regulators. For example, see C. K. Tse, “Circuit Theory and Design of Power Factor Correction Power Supplies” IEEE Distinguished Lecture 2005, Circuits and Systems (available at http://cktse.eie.polyu.edu.hk/Tse-IEEElecture2.pdf), and M. K. H. Cheung et al., “Design and Performance Considerations of PFC Switching Regulators Based on Noncascading Structures” IEEE Transactions on Industrial Electronics, Vol. 57, No. 11, November 2010, both of which are hereby incorporated by reference herein.
The inventors have determined a need for power supplies that ameliorate one or more of the above disadvantages. The inventors have determined a particular need for power supplies suitable for solid state lighting applications.